Abstract
A single-cylinder test engine fitted with an external supercharger was operated under a supercharged Homogeneous Charge Compression Ignition (HCCI) combustion process, and light emission and absorption behavior in the combustion chamber was analyzed on the basis of spectroscopic measurements. The purpose of this study was to obtain fundamental knowledge of the autoignition and combustion mechanisms in a supercharged HCCI engine. Light emission and absorption spectra in the combustion chamber were measured and analyzed for different intake air pressure levels while keeping the quantity of injected fuel constant. The results revealed clear detection of the light emission and absorption spectra of the cool flame in the low-temperature oxidation reactions. Increasing the intake air pressure while keeping the quantity of injected fuel constant resulted in a leaner air-fuel mixture. Light emission and absorption by the cool flame became more active at that time. In other words, supercharging had the effect of promoting more active cool flame reactions. On the other hand, a leaner mixture lowered the peak light emission intensity and peak heat release rate during the main combustion period, indicating that the main combustion process was moderated.
KEYWORDS – Homogeneous Charge Compression Ignition (HCCI), Supercharging, Combustion, Autoignition, Spectroscopic Measurement